The present invention relates generally to devices that can be used in conjunction with existing optical imaging devices, such as operating room microscopes, for the purpose of measuring small dimensions and in vivo (non-invasively). The present invention relates particularly to a device that exploits the transfer function of an optical imaging device to determine dimensions associated with a source object from the projected image of the source object.
Many surgical procedures are carried out by observation of the surgical field through optical instruments of various types such as operating room microscopes. Both diagnostic and surgical procedures also make extensive use of other optical instruments, such as endoscopes. Such devices provide a magnified image of the patient's anatomical structures. It is desirable to determine the dimensions of anatomical features in the field of the instrument. This is particularly true of procedures carried out in the constricted confines of some surgical fields such as the middle ear. However, such measurements are not easily accomplished.
For example, it is known to use calibrated reticules on an optical instrument to measure lateral dimensions. Changes in the position of the object being imaged with respect to the optical instrument however requires recalibration which is not practical in a surgical setting.
Lateral measurements through an endoscope have been made using twin diode lasers to project parallel beams into the image plane of the endoscope to form two spots in the field of view. Since the distance between the spots is fixed this provides a reference scale in the field of view. Herzon, G. D., et al., "New Laser Ruler Instrument for Making Measurements Through an Endoscope," Otolaryngology-Head and Neck Surgery, Vol. 116, p. 689-692 (June 1997).
Devices employing projected parallel light beams to measure the distance to an object are known. For example, U.S. Pat. No. 4,271,829 issued to Heckele discloses a device using two thin parallel visible light rays to measure the distance from the subject to the objective lens of the optical system of an endoscope. Such a device is also disclosed by Kawahara (U.S. Pat. No. 3,817,619; U.S. Pat. No. 3,817,631; and U.S. Pat. No. 3,595,220).
While devices such as graduated reticules are known for making lateral measurements through a surgical optical instrument such as an endoscope or operating room microscope or measurements of the distance of an object from the optical instrument, it is also desirable to measure anatomical structures in three-dimensional space.